Electrode



April 1934- F. HOTCHNER 1,953,608

ELECTRODE Filed Aug. 14, 1928 a INVENTOR Patented Apr. 3, 1934 EIECTBODE Fred Hotolmer, Loo Angelel, Calif. Application August 14, 1928, Serial No. 299,481

This invention relates to an electrode for gaseous conductor tubes, and has for its object to provide means to preventv the vaporization of the material of the electrodes to a degree or in a manner detrimental to the life of the tube, and the consequent occlusion on the walls of the tube of the gaseous content with the vaporized material.

The phenonema in a gaseous discharge tube are very complicated and not to this date thoroly understood. A great many distinct physical forces are at play, some very obscure, and as there are many possible conditions that can not be separated for observation but must be observed as they develop among other changing conditions, it it difiicult to trace any effect back to a definite cause.

In my attempts to improve an electrode for a discharge tube, I have found little comfort in accepted theories of the action in the tubes. The limiting factor in the life of a tube is the disappearance of the gas by occlusion, apparently on the walls of the tube by vaporized material from the electrodes at the times when they are acting as cathodes. It has been accepted that this action is always going on with a cold cathode tube, and when the size of the electrode for a given current is below a certain area that the vaporization increases enormously and the life of the tube is very short. This has been ascribed to the bombardment of the cathode by positive ions falling thru the voltage of the cathode dark space. This apparently is an inherent characteristic of a cold cathode tube, and well it might be, but I have observed great differences between various tubes in regards to the amount of deposition and even between the two electrodes of the same tube; and further, I have observed that in general the deposition is out of all proportion to what might be expected from the extremely small dimension of the fall space or from the amount of work being done in transferring the energy from the electrode to the gas. When it is considered that the pressures used in these tubes range from two to twelve millimeters of mercury it might be expected that if the present theory of vaporization is correct, that the amount of observed deposition would show some relation to the pressure. The best manner of observing this is during the pumping operation when the electrode can be observed under bombardment under all pressures within the illumination range. With all due consideration to the many other variable factors, I have 55 not from experience observed any such relationship but rather have observed effects that lend weight to the belief that some other and far more important force is at play.

Therefore I have assumed that the theory is either incorrect or incomplete. In endeavoring 00 to design an improved electrode I have aimed to arrest at some point the series of events leading to disappearance of the gas in the tube without interrupting the series of events whereby the radiation is generated from the electric energy. I have aimed to discover any consequent result from such an interruption of the events in the operation of the tube that may be turned to advantage for increased emciency or better construction. These efforts have met with success and have resulted in the construction of a discharge tube in which several desirable objects are accomplished, which are:

The construction of a tube in which the electron density around the cathode is increased and the cathode drop is reduced resulting in greater elliciency.

A discharge tube in which the electrode terminals are small and compact and lend themselves to installation in small spaces.

A discharge tube that will not readily light by one terminal excitation.

A discharge tube in which the deposition of the material on the walls of the tube is arrested.

In Figure 1 I illustrate a tube built according to this invention and connected to a transformer, and in Figure 2 I illustrate an improvement in the same in which I have eliminated the extra wire to each electrode necessary with the construction shown in Figure 1 to provide the reverse potential.

Numeral 1 indicates a discharge 'tube, 2 and 3 indicate the enlarged electrode portions of the tube, 4 and 5 indicate the glass stems for holding the electrodes 6 and 'l, whichare supplied with current by the sealed-in lead wires 8 and 9. 10 and 11 are shields outside of the glass of the tube and tightly secured thereto. 12 is a high-potential transformer. The terminals Y13 and 14 of the high voltage coil of the transformer are connected to the electrodes 6 and 7 in the order stated, and in reverse order to the corresponding shields 10 and 11. During operation, therefore the shields are always of reverse polarity to the electrodes. 1

In order to understand the operation of this device, I will recite the commonly accepted theory or cold cathode operation in a gaseous atmosphere. Upon the application of potential at gaseous atmosphere behaves as a dielectric under 110 which we are not here concerned.

strainandanelectricfleldexiststhmcutthe structure. when the potential reaches a sumciently high value electrons are withdrawn from the cathode under the influence oi the field with suflicient energy to ionize the gas, this ionization taking place first at a measurable distance from the cathode. The electrons thus produced, at least in part, move to continue the conduction or the current into the positive column, with The positive ions thus produced fall thru the potential of the dark space with increasing velocity striking it with suilicient force to vaporize the surface of the electrode and throw cflf particles. These particles, leaving the electrode with a negative charge accumulate atoms of the gas and become deposited on the walls of the tube and there occlude the gasimtilthepressureinthetubeissoreduced as to render it useless.

Here the theory seems to stop and leave much The best solution so far ciiered has been to make the surface or the cathode very large, at least above a certain critical value where the cathode drop changes rapidly and preferablyiruntentotwentytimesasgreat. Evenat this extreme a certain amoimt of deposition takes placeandthetubeswilldieintime.1tisconceivahle, however, that by moving in the opposite direction and making the electrodes extremely small that the electron density could be made great enough to break down the cathode drop and tend to greater eiiiciency. The large, bulky electrodes would also be eliminated and more compact installations result. Success in this direction depends on increasing the current density and arresting the vaporization, a result directly in conflict with current theories, but a result which I have accomplished, in fact, my tubes appear to operate better with electrodes considerahly below the critical area of vaporization.

By current density, I mean the ratio of the amountoicurrentflowinginthetubetothe area of the electrode or, more specifically, the number of ampcres per unit area of electrode. The term-critical area of vaporization-is in itslmlalacceptedsensetakentcmeanthatarea of electrode for a given current at which the cathode drop changes most rapidly. This area is indicated in the operation of the tube by the area. covered by the cathode glow, and when substantially the entire area of the electrode is covered by the cathode glow, that electrode may be understood as having the critical area of vaporization for the amount of current then flowing in the tube.

Imganddiillctfltresearchwillnodoubtbe todisccvertheprecise actioninmy tubes, astheresultssecuredmightbe duetoany one of several conditions or any combination of them, and it is quite possible that the sequence of events in my tubes are entirely diiferent than thoserecitedabove. Intheflrstcase,itispcssible that I have prevented the positive ions from fallingthruthedarkspace, orthevaporizedparticles are repelled and caused to return to the cathode. It is also pcsible that the velocity of the vaporfled particles is merely reduced allowing the changing of potential by the alternating current to prevent the completion of the series of events leading to the deposition of the gas.

The explanation I make in view of the behavior ofthetubeisasiollows. Whenthe tubeisfirst lightedduringtheprocmsofpumpingasmall amount of deposition takes place on the inside dtheglassarmmdtheelectrode. Thismetal cooperates with the glass and the shield to form a condenser having the same sign as the elec-- trode. The positive ions produced at the edge of the dark space are prevented from moving towards the cathode in great numbers. It is here that the conflict with current theory exists for it has been strongly asserted that this positive ion bombardment is absolutely necessary for the continued production of electrons from the cathode. It appears that in this tube electrons in suflicient quantity are produced without positive ion bombardment for it is to be observed that in the direction of the axis of the tube strongly defined dark and light areas exist such as might define the regions of different velocity of a stream of electrons. It appears therefore that electrons are being drawn out of the end of the cathode with suflicient velocity and in suflicient number to prevent positive ion bombardment in this direction. We have then conditions approaching hot cathode operation with a cold cathode, u very unusual, unlocked for and very valuable result. It is to be noted that no deposition takes place in the direction of this stream.

The improvement shown in Figure 2 provides means to eliminate the extra reverse-potential wire shown to each electrode in Figure l. The numeral 20 indicates the end of a tube and 21 the electrode portion which might be of the same diameter if desired. 22 indicates the electrode; 23, the glass stem; 24, the sealed-in lead wire. and 25, a feed wire from the transformer. The region of preliminary deposition within the tube is indicated by 26. 27 indicates a shield surrounding the tube; 28, a. dielectric g cylinder surrounding the shield 27, and 29, a shield surrounding the dielectric cylinder 28. The shield 29 is connected to the lead wire 24. The eifect of this arrangement is the same as that shown in the first figure and much more 5 practicable.

It is further noted that this tube has a very desirable characteristic as an electrical device in that when one terminal is connected to one terminal of a transformer it is very difiicult to 129 illuminate the tube any appreciable degree. The reason for this is not easily found but is no doubt due in some respect to the condenser action of the electrode. This result is desirable because in flashing the tubes it eliminates the necessity 1 5 of disconnecting both terminals from the circuit.

It is well known that in cold cathode tubes a considerable loss of energy takes place at the cathode. From the reasoning which I have given above it might be expected that if I have 139 actually broken down in some measure the cathode drop that this loss of energy will be reduced and some evidence of it can be discovered. Here again, considerable research is necessary to secure actual figures, but the evidence that is sufllcient from a commercial point of view would be the actual footage of tubing that can be lighted from a given transformer as compared with large, cold cathode tubes. Regardlem of the scientific explanation that might be made it is quite evident from the tests that a greater footage of tubing can be lighted with tubes equipped with my electrodes.

It is to be understood that this invention is not to the particular construction shown and that it is applicable as well to discharge tube 145 in which the conducting atmosphere consists in whole or in part of metallic vapors.

Having thus described my invention, what 1 claim as new and desire to secure by Letters Pateat is:

Hill

2. In a discharge tube having an internal electrode, conductive means inside and outside the walls 01' said tube in the region of said electrode and means to apply a potential 01' opposite sign to that of said electrode to said outside conductive means.

FRED HOTCHNER. 

